The delivery of radionuclides to different organ and tissue targets has been the objective of many research efforts for both diagnostic and therapeutic purposes. Various molecules have been tried that would carry the active component to the desired site and yet be stable at least until the site has been reached by the delivery system. Halogenated (e.g. .sup.131 I and .sup.88m Br) organic molecules have been used. Thus iodinated hippuran has been used to study renal function, e.g. J. Nucl. Med. 23, 377-380 (1982). Also labeling a monoclonal antibody with .sup.131 I has been proposed for the detection and therapy of cancer, e.g. Cancer Res. 44, 5744-5751 (1984).
Metallic radionuclides offer a variety of nuclear properties and chemistries. Thus, for example, .sup.201 Tl, .sup.67 Cu, .sup.99m Tc, .sup.90 Y and various isotopes of In and Ga are only a few examples of radioiosotopes that have been used for diagnostic imaging and/or therapy. Of these metals, the chemistry of .sup.99m Tc has been explored the most for use as a radiopharmaceutical. For example, Tc-diphosphonates are used to image the skeletal system [see Subramanian et al., Radiology 149, 823-828 (1983)]. Loberg et al. [J. Nucl. Med. 16, 533 (1975)] were able to study liver function with lipophilic .sup.99m Tc complexes in which the Tc existed in a +3 oxidation state and the overall charge of the iminodiacetic acid complex was -1. Deutsch et al. [Science 213, 85 (1981)] was able to prepare Tc complexes with As and P containing ligands that localized in the heart. These compounds contained a Tc(III) core with an overall charge of the complex of +1. Also Volkert et al. [Int'l. J. Appl. Rad. Isotopes 35, 467-470 (1974)] were successful in delivering Tc(III) to brain tissue.
However, since .sup.99m Tc is a pure gemma emiter, it is limited only to diagnostic applications. Therefore, there has been a need for particle emitting radioisotope complexes and/or conjugates which would be useful in therapy. Deutsch et al. [Corina Int'l., Veronai and Raven Press, pp. 733-740 (1990)] have used the combination of .sup.186 Re and a diphosphonate to treat bone tumors. Also Simon et al. (U.S. Pat. No. 4,898,724) teach the use of .sup.153 Sm and other rare earth radionuclides in combination with aminophosphonic acids for the treatment of bone pain and tumors.
The development of bone metastasis is a common and often catastrophic event for a cancer patient. The pain, pathological fractures, frequent neurological deficits and forced immobility caused by these metastatic lesions significantly decrease the quality of life for the cancer patient. The number of patients that contract metastatic disease is large since nearly 50% of all patients who contract breast, lung or prostate carcinoma will eventually develop bone metastasis. Bone metastasis are also seen in patients with carcinoma of the kidney, thyroid, bladder, cervix and other tumors, but collectively, these represent less than 20% of patients who develop bone metastasis. Metastatic bone cancer is rarely life threatening and occasionally patients live for years following the discovery of the bone lesions. Initially, treatment goals center on relieving pain, thus reducing requirements for narcotic medication and increasing ambulation. Clearly, it is hoped that some of the cancers can be cured.
The use of radionuclides for treatment of cancer metastatic to the bone dates back to the early 1950's. It has been proposed to inject a radioactive particle-emitting nuclide in a suitable form for the treatment of calcific lesions. It is desirable that such nuclides be concentrated in the area of the bone lesion with minimal amounts reaching the soft tissue and normal bone. Radioactive phosphorus (P-32 and P-33) compounds have been proposed, but the nuclear and biolocalization properties limit the use of these compounds. (E. Kaplan, et al., J. Nucl. Med. 1(1), 1, (1960); U.S. Pat. No. 3,965,254).
Another attempt to treat bone cancer has been made using phosphorus compounds containing a boron residue. The compounds were injected into the body (intravenously) and accumulated in the skeletal system. The treatment area was then irradiated with neutrons in order to activate the boron and give a therapeutic radiation dose. (U.S. Pat. No. 4,399,817).
The use of Re-186 complexed with a diphosphonate has also been proposed. [L. Mathieu et al., Int. J. Applied Rad. & Isotopes, 30, 725-727 (1979); J. Weinenger, A. R. Ketring et al., J. Nucl. Med., 24(5), P125 (1983)]. However, the preparation and purification needed for this complex limits its utility and wide application.
Strontium-89 has also been proposed for patients with metastatic bone lesions. However, the long half-life (50.4 days), high blood levels and low lesion to normal bone ratios limit the utility. [N. Firusian, P. Mellin, C. G. Schmidt, J. Urology, 116, 764 (1976); C. G. Schmidt, N. Firusian, Int. J. Clin. Pharmacol., 93, 199-205, (1974)].
A palliative treatment of bone metastasis has been reported which employed I-131 labeled .alpha.-amino-(3-iodo-4-hydroxybenzylidene)diphosphonate [M. Eisenhut, J. Nucl. Med., 25(12), 1356-1361 (1984)]. The use of radioiodine as a therapeutic radionuclide is less than desirable due to the well known tendency of iodine to localize in the thyroid. Eisenhut lists iodide as one of the possible metabolites of this compound.
The use of radionuclides for calcific tumor therapy or relief of bone pain is discussed in published European patent application 176,288, where the use of Sm-153, Gd-159, Ho-166, Lu-177 or Yb-175 complexed with a ligand such as ethylenediaminetetraacetic acid (EDTA) or hydroxyethylenediaminetriacetic acid (HEEDTA) is disclosed. A macrocyclic system having a 1,4,7,10-tetraazacyclododecane moiety complexed with Sm-153, Gd-159, Ho-166, Lu-177 or Yb-175 for calcific tumor therapy or relief of bone pain is discussed in U.S. Pat. No. 5,059,412 which complex is very stable and has a lower charge than the complex disclosed in published European patent application 176,288.
Functionalized chelants, or bifunctional coordinators, are known to be capable of being covalently attached to an antibody having specificity for cancer or tumor cell epitopes or antigens. Radionuclide complexes of such antibody/chelant conjugates are useful in diagnostic and/or therapeutic applications as a means of conveying the radionuclide to a cancer or tumor cell. See, for example, Meares et al., Anal. Biochem. 142, 68-78, (1984); and Krejcarek et al., Biochem. and Biophys. Res. Comm. 77, 581-585 (1977).
Aminocarboxylic acid chelating agents have been known and studied for many years. Typical of the aminocarboxylic acids are nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), hydroxyethylethylenediaminetriacetic acid (HEDTA), diethylenetriaminepentaacetic acid (DTPA), trans-1,2-diaminocyclohexanetetraacetic acid (CDTA) and 1,4,7,10-tetraazacyclododecanetetraacetic acid (DOTA). Numerous bifunctional chelating agents based on aminocarboxylic acids have been proposed and prepared. For example the cyclic dianhydride of DTPA [Hnatowich et al. Science 220, 613-615, (1983); U.S. Pat. No. 4,479,930] and mixed carboxycarbonic anhydrides of DTPA [Gansow, U.S. Pat. Nos. 4,454,106 and 4,472,509; Krejcarek et al., Biochem. and Biophys. Res. Comm. 77, 581-585, (1977)] have been reported. When the anhydrides are coupled to proteins the coupling proceeds via formation of an amide bond thus leaving four of the original five carboxymethyl groups on the diethylenetriamine (DETA) backbone [Hnatowich et al. Int. J. Appl. Isot. 33, 327-332, (1982)]. In addition, U.S. Pat. Nos. 4,432,907 and 4,352,751 disclose bifunctional chelating agents useful for binding metal ions to "organic species such as organic target molecules or antibodies." As in the above, coupling is achieved via an amide group through the utilization of diaminotetraacetic acid dianhydrides. Examples of anhydrides include dianhydrides of EDTA, CDTA, propylenediaminetetraacetic acid and phenylene 1,2-diaminetetraacetic acid. A recent U.S. Pat. No. 4,647,447 discloses several complex salts formed from the anion of a complexing acid for use in various diagnostic techniques. Conjugation via a carboxyl group of the complexing acid is taught which gives a linkage through an amide bond.
In the J. Radioanal. Chem. 57(12), 553-564 (1980), Paik et al. disclose the use of p-nitrobenzylbromide in a reaction with a "blocked" diethylenetriamine, i.e. bis-(2-phthalimidoethyl)amine followed by deblocking procedures and carboxymethylation using chloroacetic acid, to give N'-p-nitrobenzyldiethylenetriamine N,N,N",N"-tetraacetic acid. Again, since the attachment is through a nitrogen, a tetraacetic acid derivative is obtained. Conjugation of the bifunctional chelating agent and chelation with indium is discussed. Substitution on the nitrogen atom is also taught by Eckelman, et al. in the J. Pharm. Sci. 64(4), 704-706 (1975) by reacting amines such as "ethylenediamine or diethylenetriamine with the appropriate alkyl bromide before carboxymethylation." The compounds are proposed as potential radiopharmaceutical imaging agents.
Another class of bifunctional chelating agents based on aminocarboxylic acid functionality is also well documented in the literature. Thus, Sundberg, Meares, et al. in the J. Med. Chem. 17(12), 1304 (1974), disclosed bifunctional analogs of EDTA. Representative of these compounds are 1-(p-aminophenyl)-ethylenediaminetetraacetic acid and 1-(p-benzenediazonium)ethylenediaminetetraacetic acid. Coupling to proteins through the para-substituent and the binding of radioactive metal ions to the chelating group is discussed. The compounds are also disclosed in Biochem. and Biophys. Res. Comm. 75(1), 149 (1977), and in U.S. Pat. Nos. 3,994,966 and 4,043,998. It is important to note that the attachment of the aromatic group to the EDTA structure is through a carbon of the ethylenediamine backbone. Optically active bifunctional chelating agents based on EDTA, HEDTA and DTPA are disclosed in U.S. Pat. No. 4,622,420. In these compounds an alkylene group links the aromatic group (which contains the functionality needed for attachment to the protein) to the carbon of the polyamine which contains the chelating functionality. Other references to such compounds include Brechbiel et al., Inorg. Chem. 25, 2772-2781 (1986), U.S. Pat. No. 4,647,447 and International Patent Publication No. WO 86/06384.
More recently, certain macrocyclic bifunctional chelating agents and the use of their copper chelate conjugates for diagnostic or therapeutic applications have been disclosed in U.S. Pat. No. 4,678,667 and by Moi et al., Inorg. Chem. 26, 3458-3463 (1987). Attachment of the aminocarboxylic acid functionality to the rest of the bifunctional chelating molecule is through a ring carbon of the cyclic polyamine backbone. Thus, a linker, attached at one end to a ring carbon of the cyclic polyamine, is also attached at its other end to a functional group capable of reacting with the protein.
Another class of bifunctional chelating agents, also worthy of note, consists of compounds wherein the chelating moiety, i.e. the aminocarboxylic acid, of the molecule is attached through a nitrogen to the functional group of the molecule containing the moiety capable of reacting with the protein. As an example, Mikola et al. in patent application (WO 84/03698, published Oct. 27, 1984) disclose a bifunctional chelating agent prepared by reacting p-nitrobenzylbromide with DETA followed by reaction with bromoacetic acid to make the aminocarboxylic acid. The nitro group is reduced to the corresponding amine group and is then converted to the isothiocyanate group by reaction with thiophosgene. These compounds are bifunctional chelating agents capable of chelating lanthanides which can be conjugated to bio-organic molecules for use as diagnostic agents. Since attachment of the linker portion of the molecule is through one of the nitrogens of the aminocarboxylic acid, then one potential aminocarboxyl group is lost for chelation. Thus, a DETA-based bifunctional chelant containing four (not five) acid groups is prepared. In this respect, this class of bifunctional chelant is similar to those where attachment to the protein is through an amide group with subsequent loss of a carboxyl chelating group.
Recently Carney, Rogers, and Johnson disclosed (3rd. Int'l. Conf. on Monoclonal Antibodies for Cancer: San Diego, Calif.--Feb. 4-6, 1988) abstracts entitled "Absence of Intrinsically Higher Tissue Uptake from Indium-111 Labeled Antibodies: Co-administration of Indium 111 and Iodine-125 Labeled B72.3 in a Nude Mouse Model" and "Influence of Chelator Denticity on the Biodistribution of Indium-111 Labeled B72.3 Immunoconjugates in Nude Mice". The biodistribution of indium-111 complexed with an EDTA and DTPA bifunctional chelating agent is disclosed. Attachment of the aromatic ring to the EDTA/DTPA moieties is through an acetate methylene. Also at a recent meeting D. K. Johnson et al. [Florida Conf. on Chem. in Biotechnology, Apr. 26-29 (1988), Palm Coast, Fla.] disclosed bifunctional derivatives of EDTA and DTPA where a p-isothiocyanatobenzyl moiety is attached at the methylene carbon of one of the carboxymethyl groups. Previously Hunt et al. in U.S. Pat. Nos. 4,088,747 and 4,091,088 (1978) disclosed ethylenediaminediacetic acid (EDDA) based chelating agents wherein attachment of an aromatic ring to the EDDA moiety is through the alkylene or acetate methylene. The compounds are taught to be useful as chelates for studying hepatobiliary function. The preferred metal is technetium-99m. Indium-111 and indium-113m are also taught as useful radionuclides for imaging.
Such uses of other complexes are known using radio frequency to induce hyperthermia (Japanese Kokai Tokkyo Koho JP 61, 158,931) and fluorescent-Immunoguided therapy (FIGS) [K. Pettersson et a., Clinical Chem. 29(1), 60-64 (1983) and C. Meares et al., Acc. Chem. Res. 17, 202-209 (1984)].
Consequently, it would be advantageous to provide a complex that does not readily dissociate, that exhibits rapid whole body clearance except from the desired tissue, and conjugates with an antibody to produce the desired results.